1. Field of the Invention
The present invention relates to container capping machines. The invention is directed to an improved apparatus for placing caps into contact with their containers and rotating the caps onto the containers.
2. Description of the Prior Art
Bottle capping machines using the current art have been existence for over 20 years. An example of apparatus disclosing the state of the prior art is applicant's rotary chuck capper, Model No. NERCC-8 (prior to 1992). Prior art technology teaches the advancement of a container along a predetermined path until it is aligned with a spindle assembly of a capping machine. A cam follower is connected to the spindle so that as the cam follower moves along a cam having a varying elevation the spindle assembly moves up and down along a vertical axis as directed by the cam and cam follower. A compression spring applies a downward force to the spindle assembly, adding to the downward force caused by the weight of the spindle assembly, to ensure that the cam follower rides snugly on the cam. The bottom end of the spindle is attached to a collet housing to which is attached a collet. The collet captures a container cap for application to a container. When the generally vertical axis of the container becomes aligned with the generally vertical axis of the cap, the elevation of the cam decreases and the cam follower moves downwardly on the cam. This causes the spindle to move downwardly so that the cap engages the open end of the container. The weight of the spindle assembly plus the downward force provided by the compression spring causes the threads of the cap to push downwardly on the threads of the container. This downward force is difficult to control and often causes damage to the container threads, such as cross threading, stripping of the threads and collapse of the open end of fragile containers. Attempts were made to solve the problem by mounting a compression spring to the spindle assembly to apply an upward force to counteract the downward force caused by the first compression spring and the weight of the spindle assembly. This has not been entirely successful as damage to the containers and to the container threads still occurs. The springs do not apply a uniform force during their extension or compression as the spindle assembly moves downwardly to position the cap on the container and during the rotation of the cap onto the threads of the container frequently creating too much downward force. Selective adjustment of the tension or compression forces in the springs to close tolerances is difficult if not impossible. Therefore it is clear that there is a need for an apparatus that will apply a constant, light, downward force on the spindle throughout its movement. The apparatus must be selectively adjustable to allow light engagement of the cap and container threads and to provide light contact between the threads during rotation of the cap. This apparatus should also allow for quick adjustment when switching to production runs for containers and caps of different sizes and with different numbers of threads per inch. The apparatus should also be adaptable for easy exchange of collets for gripping the different sized caps.
A container capping machine having this improvement will be more efficient by reducing the number of damaged products, reducing the down time for change over, and reducing the number of work stoppages due to damaged products. Such an improvement will also provide the capability of using containers that have thin, flexible or fragile walls adjacent the container mouth.